The present invention relates to a tail pipe structure of a control type muffler.
As an example of a control type muffler having a control valve opening and closing in proportion to the number of revolutions of the internal combustion engine, there has been known one that is disclosed in Japanese Laid-open Utility Model Publication No. 61-126022.
FIG. 3 shows this kind of control type muffler. Its structure is such that expansion chambers 17, 19 and 21 and a resonance chamber 23 are defined by partition plates 11, 13 and 15. Further, an outlet pipe 27 having a control valve 25 opens in the expansion chamber 19 and a bent outlet pipe 29 opens into the expansion chamber 21. In the figure, reference numeral 31 designates an inlet pipe, reference numeral 33 designates a resonator pipe and reference numerals 35 and 37 designate inner pipes, respectively.
In the case of the control type muffler of the above-described structure, when the number of revolutions of the engine is less than the set value (low speed), the control valve 25 is closed by a control device 39 and generally low frequency noises reduce at a high exhaust pressure. When the engine speed is higher than the set value (high speed), the valve 25 is opened by the control device 39 and generally high frequency vibrations reduce at a low exhaust pressure.
However, such conventional control type muffler has had problems that due to the fact that the control valve 25 is closed by the control device 39 when the number of engine revolutions is less than the set value, the exhaust gases are discharged into the atmosphere only through the outlet pipe 29 instead of the outlet pipe 27, those who have no knowledge of the mechanism are liable to conclude by mistake that the exhaust system is out of order
Further, there has been another problem that in a cold district, the open end of the outlet pipe 27 is adhered with snow or becomes frozen so that it is not possible to thaw the snow or ice until the control valve 25 opens.
The present invention has been made to solve the above problems and it is an object of the invention to provide a tail pipe structure of a control type muffler which allows exhaust gases to be discharged from the outlet pipe having a control valve even when the valve is closed.
In the case of the present invention, the downstream side of the control valve of the second outlet pipe through a communication pipe and therefore, when the control valve is closed, the exhaust gases are discharged into the atmosphere from the first outlet pipe while part of the exhaust gases flow from the first outlet pipe into the second outlet pipe via the communication pipe and is then discharged into the atmosphere.
Accordingly, even when the control valve is closed, it is possible for the exhaust gases to be discharged into the atmosphere through the first and second outlet pipes.